The three methods of atomic power, thermal power, and hydraulic power generation, are now used as main power generation methods, and from a viewpoint of resource quantity and energy density, the three power generation methods are also expected to be used as main power generation methods in the future. Especially, since thermal power generation is safe, and its utility value is high as a power generation method with a high capacity to respond to load changes, it is expected that the thermal power generation will also continue to play an important role in the power generation field in the future.
In general, a steam turbine facility, which is used in a coal-fired power station including steam turbines, is provided with a high-pressure turbine, an intermediate-pressure turbine, and a low-pressure turbine. In such a steam turbine facility, steam with a temperature in the 600° C. or lower class is used. A rotor and a casing of the high-pressure turbine or the intermediate pressure turbine, which is exposed to a high temperature, are formed from a ferrite-based material which has a thermal resistance to steam with a temperature in the 600° C. or lower class, excellent manufacturability and is economically competitive.
Recently, however, in order to reduce emissions of CO2 and improve thermal efficiency a technique which adopts steam conditions in the 650° C. or 700° C. class is being demanded. Patent Document 1 has disclosed a steam turbine facility capable of operating at a high temperature in which a reheat steam condition is 650° C. or higher.
FIG. 4 is a schematic system view illustrating a conventional steam turbine facility disclosed in Patent Document 1. In the steam turbine facility 110 illustrated in FIG. 4, the intermediate-pressure turbine is separated into a first intermediate-pressure turbine 112 on a high-temperature and high-pressure side and a second intermediate-pressure turbine 114 on a low-temperature and low-pressure side. Additionally, the high-pressure turbine 116 and the second intermediate-pressure turbine 114 are integrated to form an integrated structure 122. The integrated structure 122 is connected on the same axis as the first intermediate-pressure turbine 112 on a high-temperature and high pressure side, the low-pressure turbine 124, and the generator 126.
Main steam superheated to a temperature in the 600° C. class by a boiler 132 is introduced into the high-pressure turbine 116 through a main steam pipe 134. The steam introduced into the high-pressure turbine 116 performs expansion work and is then exhausted and returned to the boiler 132 through a low-temperature reheat pipe 138. The steam returned to the boiler 132 is reheated by the boiler 132 such that the temperature thereof increases to the 700° C. class. The reheated steam is sent to the first intermediate-pressure turbine 112 through a high-temperature reheat pipe 140. A rotor of the first intermediate-pressure turbine 112 is formed from a material (austenitic heat resisting steel) capable of withstanding steam heated to a high temperature in the 700° C. class. The steam sent to the first intermediate-pressure turbine 112 performs expansion work and is then exhausted and sent to the second intermediate-pressure turbine 114 through an intermediate-pressure part connection pipe 142 in a state where the temperature thereof decreased to the 550° C. class. The steam sent to the second intermediate-pressure turbine 114 performs expansion work and is then exhausted and introduced to the low-pressure turbine 124 through a crossover pipe 144. The steam introduced into the low-pressure turbine 124 performs expansion work and is then exhausted and sent to a condenser 128. The steam sent to the condenser 128 is condensed by the condenser 128, and is then returned to the boiler 132 in a state where the pressure thereof is raised by a water feed pump 130. The generator 126 is rotationally driven by the expansion work of the respective turbines to generate power.
In such a steam turbine facility, the intermediate-pressure turbine is divided, and only the first intermediate-pressure turbine 112 is formed from a material capable of withstanding steam with a temperature of 650° C. or higher. Therefore, a steam condition of 650° C. or higher may be adopted, and the amount of the material capable of withstanding steam with a temperature of 650° C. or higher used may be reduced. Therefore, it is possible to reduce the manufacturing costs of the entire facility.
In the technique disclosed in Patent Document 1, however, when a steam turbine facility with large capacity is considered, the facility illustrated in FIG. 4 is difficult to implement. When such a material as Ni-based alloy capable of withstanding steam with a temperature of 650° C. or higher is used to form the first intermediate-pressure turbine 112, it is difficult to manufacture a turbine rotor or casing weighing 10t or more in terms of the limitation of material manufacturing, and it is impossible to manufacture a large-sized turbine rotor or casing.
Therefore, as illustrated in FIG. 5, the first intermediate-pressure turbine may be further divided into primary and secondary first intermediate-pressure turbines 112 and 113. In this case, however, the number of casings increases, and thus the number of buildings or pipes increases. Therefore, the manufacturing costs of the facility inevitably increases. Additionally, as the number of shafts (divided turbines) increases, it is highly likely that vibrations occur.
Additionally, a ferrite-based material may be used instead of using the Ni-based alloy. In this case, however, a large amount of cooling steam needs to be introduced into the casings. As a result, the internal efficiency of the turbines decreases.